Conventionally, an electronic component mounting machine for mounting electronic components on a board employs a component positioning method applying visual recognition technology. An example of conventional component detection methods is described by referring to the drawings.
FIGS. 20-25 show a conventional component detection method. FIGS. 20 and 21 show as an example a method for finding the center of gravity G of a shade pattern of a component 10 imaged as a shade image, and determining it as the center of the component.
FIGS. 22-25 show another example of the prior art. This example first finds the moment and the center of gravity G of a shade pattern of a component 10 imaged as a shade image (FIG. 23). In FIG. 23, .theta. is a deflection angle of the component 10 which is found by an ellipse approximation method shown in FIG. 27. Then, end point detection windows 67a, 67b, 67c, and 67d are established at four points on the component 10 based on the size, the moment, and the center of gravity G, and end points of the component 68a, 68b, 68c, and 68d in each window are determined (FIG. 24). Subsequently, the centerline of component 19 is determined from four end points of the component (FIG. 25).
However, the methods as described above are easily affected by the shape and color of the component, irregularity on the surface of component, or brightness or darkness caused by how illuminance is projected on the component. Thus, there is a problem that there arises offset between the actual centerline of the component and that obtained through recognition, so that accuracy is deteriorated. FIG. 26 shows the situation where the outline of an imaged component 10 is distorted by the above effects. If the end points of the component 68a-68d are determined by establishing the conventional windows 67a-67d, they are positioned as shown in FIG. 26. The centerline of component 19 obtained on the basis of above result would be offset from the true centerline of component 19a.
In view of the above problems, the present invention is intended to provide a method for detecting a centerline of component or the like for an electronic component mounting machine which is less affected by the state of components or the environment.